95 Blazer brake problem, Power booster?

Yesterday driving to work brakes were fine. Then about 5 hours later I go to lunch and they are fine till I get back and im about to park they all of a sudden got very hard to press. Its like trying to brake with the car turned off. Fluid is full, pulled the hose off the power booster that leads to engine and heard a burst of air. (while car was off). When at idle and press brakes it does mess with the idle. No tach so dont know what rpms are at but sounds like they jump up when press breaks at idle. Any Help?

95 Chevy Blazer 4.3 vortec 4x4 vin W

sounds like either a loss of vacuum or fluid pressure.

Pretty sure its loss of vacuum i can hear a hissing sound when i hit the breaks coming from the inside like under the dash. also since the idle jumps around just putting my foot on the break makes me think that to. I changed the spark plugs and while the tires were off looked at the break lines they seemed to be fine. still stops fine just really hard.

I hate to bring up an old thread, but I have been going out of my mind with the same problem. The brakes are very hard, like there is no boost. I have replaced pretty much everything in the system, including the booster and master cylinder, but still the same problem.

Did you ever get this fixed?

I hate to bring up an old thread, but I have been going out of my mind with the same problem. The brakes are very hard, like there is no boost. I have replaced pretty much everything in the system, including the booster and master cylinder, but still the same problem.

Did you ever get this fixed?

Did you replace the check valve on the end of the vacuum line that plugs into the booster?